U.S. patent number 7,491,860 [Application Number 11/196,033] was granted by the patent office on 2009-02-17 for dehydrogenation process.
This patent grant is currently assigned to Sud-Chemie Inc.. Invention is credited to Vladimir Fridman, Andrzej Rokicki, Michael Urbancic.
United States Patent |
7,491,860 |
Fridman , et al. |
February 17, 2009 |
Dehydrogenation process
Abstract
A process for adiabatic, non-oxidative dehydrogenation of
hydrocarbons including passing a hydrocarbon feed stream through a
catalyst bed, wherein the catalyst bed includes a first layer of a
catalyst and second layer of a catalyst, wherein the catalyst of
the first layer has high activity but a higher capacity for
producing coke than the catalyst of the second layer and the second
catalyst also has high activity but a lower capacity for producing
coke than the catalyst of the first layer.
Inventors: |
Fridman; Vladimir (Louisville,
KY), Urbancic; Michael (Louisville, KY), Rokicki;
Andrzej (Mountain Lakes, NJ) |
Assignee: |
Sud-Chemie Inc. (Louisville,
KY)
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Family
ID: |
37496121 |
Appl.
No.: |
11/196,033 |
Filed: |
August 3, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070032691 A1 |
Feb 8, 2007 |
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Current U.S.
Class: |
585/663; 585/660;
585/662; 502/355; 208/134; 502/319; 502/305; 502/320 |
Current CPC
Class: |
C07C
5/3337 (20130101); B01J 23/26 (20130101); B01J
35/0006 (20130101); B01J 23/8993 (20130101); B01J
35/10 (20130101); C07C 5/333 (20130101); C07C
5/333 (20130101); C07C 11/02 (20130101); C07C
5/3337 (20130101); C07C 11/02 (20130101); B01J
35/1014 (20130101); C07C 2523/26 (20130101); C07C
2521/04 (20130101); C07C 2523/04 (20130101); B01J
37/10 (20130101); C07C 2521/06 (20130101); C07C
2523/42 (20130101); C07C 2523/755 (20130101); B01J
35/1019 (20130101); C07C 2521/10 (20130101) |
Current International
Class: |
C07C
5/333 (20060101); B01J 23/00 (20060101); C10G
35/04 (20060101) |
Field of
Search: |
;585/660,662,663
;208/133,134 ;502/305,319,320,355 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 162 082 |
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Jan 1986 |
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GB |
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WO 95/23123 |
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Aug 1995 |
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WO |
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WO 2006/124145 |
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Nov 2006 |
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WO |
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Primary Examiner: Caldarola; Glenn
Assistant Examiner: Bullock; In Suk
Attorney, Agent or Firm: Cox; Scott R.
Claims
The invention claimed is:
1. A process for the dehydrogenation of aliphatic hydrocarbons,
comprising (a) loading a first dehydrogenation catalyst in a first
layer of a catalyst bed in a reactor; (b) loading a second
dehydrogenation catalyst in a second layer of the catalyst bed in
the reactor; (c) reducing the catalysts; and (d) introducing a feed
stream to the catalyst bed, comprising an aliphatic hydrocarbon,
such that the feed stream initially contacts the catalyst in the
first catalyst layer and then the catalyst in the second catalyst
layer, wherein the first catalyst comprises a catalyst with high
activity but a higher capacity for producing coke than the catalyst
of the second layer, and the second catalyst comprises a catalyst
with the same or different activity, but a reduced capacity to make
coke from the capacity of the catalyst of the first layer, wherein
the composition of the catalysts of the first and second layers
comprises from about 70 to about 90% by weight of alumina and from
about 10 to about 30% by weight of one or more chromium compounds,
and wherein the composition of the catalysts of the first layer
contains a higher percentage of Cr.sup.+6 components, by weight,
than the catalysts of the second layer.
2. The process of claim 1, wherein the catalyst of the second layer
produces about 20 to about 80% by weight less coke than the
catalyst in the first layer.
3. The process of claim 1, wherein the chromium compounds of the
catalysts of the first layer comprise at least about 1.2% of a
Cr.sup.6+ composition, by weight.
4. The process of claim 1, wherein the chromium compounds of the
catalysts of the second layer comprise from about 0.01 to less than
1.1% by weight Cr.sup.6+ compounds, based on the total weight of
the catalyst.
5. The process of claim 1, wherein the composition of the catalyst
of the second layer further comprises at least 0.5 to about 0.7% of
Na.sub.2O by weight.
6. The process of claim 5, wherein the composition of the catalyst
of the second layer, instead of including at least 0.5 to about 0.7
weight percent of Na.sub.2O, instead comprises another alkali metal
compound on an equivalent molar basis.
7. The process of claim 1, wherein the composition of the catalyst
of the first layer further comprises from about 0.5 to about 1.7%
by weight of a nickel compound, calculated as NiO.
8. The process of claim 1, wherein the composition of the catalyst
of the first layer further comprises from about 100 ppm to about
10,000 ppm of a Pt compound.
9. The process of claim 1, wherein the composition of the catalyst
of the first layer further comprises less than 0.5% by weight of
Na.sup.2O.
10. The process of claim 9, wherein the composition of the catalyst
of the first layer, instead of including less than 0.5% by weight
Na.sub.20, instead comprises another alkali metal compound on an
equivalent molar basis.
11. The process of claim 1, wherein the surface area of the
catalyst of the first layer is greater than the surface area of the
catalyst of the second layer.
12. The process of claim 1, wherein the surface area of the
catalyst of the first layer is at least 90 m.sup.2/g.
13. The process of claim 1, wherein the surface area of the
catalyst of the first layer is greater than 90 m.sup.2/g to about
120 m.sup.2/g.
14. The process of claim 1, wherein the surface area of the
catalyst of the second layer is from about 50 m.sup.2/g to 90
m.sup.2/g.
15. The process of claim 1, wherein the catalyst of the first layer
comprises from about 85% to 50% by weight of the catalysts in the
reactor.
16. The process of claim 1, wherein the catalyst of the second
layer comprises from about 15% to less than 50% by weight of the
catalysts in the reactor.
17. The process of claim 1, wherein the catalyst of the first layer
is calcined in a steam/air atmosphere with a steam concentration no
more than 20% by volume of added steam.
18. The process of claim 1, wherein the catalyst of the second
layer is calcined in a steam/air atmosphere with a steam
concentration greater than 20 to 100% by volume of added steam.
19. The process of claim 1, wherein the catalyst of the second
layer is calcined in a steam/air atmosphere with a steam
concentration from about 80 to 100% by volume of added steam.
20. The process of claim 1, wherein the average pore size of the
pores on the catalyst of the first layer is smaller than the
average pore size of the pores on the catalyst of the second layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
None
BACKGROUND OF INVENTION
The present invention relates to an improved process for adiabatic,
non-oxidative dehydrogenation of hydrocarbons whereby a hydrocarbon
feed stream is passed through a catalyst bed containing at least a
first layer of a first catalyst and a second layer of a second
catalyst, wherein the catalyst of the first layer exhibits high
activity, but also a higher capacity to produce coke than the
second catalyst, while the catalyst of the second layer also
exhibits high activity but a reduced capacity to make coke. Various
preparation and/or treatment processes and/or differences in the
composition of the catalysts contained in the two layers can cause
the differences in capacity of the catalysts to make coke.
Alkane dehydrogenation is a recognized process for the production
of a variety of useful hydrocarbon products, such as isobutylene
for conversion to MTBE, isooctane and alkylates to supplement and
enrich gasolines and propylene for use in the polymer industry.
There are several processes recognized for the catalytic
dehydrogenation of light alkanes, including the Sud-Chemie
HOUDRY.RTM. process. The catalysts that are used in these
dehydrogenation processes may be manufactured from different
materials. For example, the HOUDRY.RTM. process normally utilizes
chromia-alumina catalysts. While not limited, the process of the
present invention is especially designed for use with the
HOUDRY.RTM. dehydrogenation process.
In the HOUDRY.RTM. process, an aliphatic hydrocarbon, such as
propane, is passed through a dehydrogenation catalyst bed, which
may contain various layers of catalysts, where the hydrocarbon
travels from one layer to the next and in the process is
dehydrogenated to its complimentary olefin. Because the
dehydrogenation reaction is endothermic and the process is
adiabatic, the temperature of the catalyst bed decreases during the
dehydrogenation cycle. At the same time, paraffin conversion
declines until conversion is no longer economical. The hydrocarbon
flow is stopped at this point. After a steam purge, the catalyst is
subjected to a regeneration cycle in air in order to remove coke
that has been deposited on the catalyst. During the regeneration
cycle the catalyst bed gains heat, some of which is produced by
burning of the coke. Thus, coke combustion plays an important role
in the heat balance in the catalyst bed. After regeneration the
catalyst is reduced, and the cycle is repeated. This process is
discussed in detail, for example in U.S. Pat. Nos. 2,419,997 and
5,510,557 and U.S. patent application Ser. No. 20040087825, which
references are incorporated herein by reference.
Due to equilibrium limitations, dehydrogenation processes require
relatively high operating temperatures. However, as the temperature
is increased, a point is reached where the production of
undesirable by-products, such as light gas and coke, is so high
that the yield of the desired olefin begins to decline.
Thus, it would be advantageous if a method could be developed for
the dehydrogenation of aliphatic hydrocarbons that improves olefin
selectivity and yield by optimizing the performance of the
catalysts of the catalyst bed, especially for production of coke,
by various methods such as by adjusting the composition and/or
performance of the catalysts contained in the catalyst bed.
SUMMARY OF THE INVENTION
The present invention provides a method for optimization of the
performance of a catalyst bed, especially for use in a
dehydrogenation process, comprising loading layers of catalysts
into a dehydrogenation catalyst bed, at least two of which exhibit
different capacities for production of coke. The composition of the
catalyst of each catalyst layer is optimized based on requirements
of heat balance and kinetics, which are different depending on the
location of the catalysts in the catalyst bed.
The present invention preferably provides a process for the
dehydrogenation of aliphatic hydrocarbons including (a) loading at
least a first and a second layer of dehydrogenation catalysts into
a catalyst bed, whereby the hydrocarbon feed first contacts the
catalysts of the first layer, wherein the catalysts of each layer
exhibit different, predetermined capacities for the production of
coke, (b) reducing the catalysts loaded in the catalyst bed with a
reducing gas, such as hydrogen, and evacuating the bed, (c)
introducing an aliphatic hydrocarbon feed stream into the catalyst
bed, such that the feed stream initially contacts the first layer
of the catalyst bed prior to contacting the second layer of the
catalyst bed, whereby the aliphatic hydrocarbon is dehydrogenated,
(d) steam purging and regenerating the catalysts contained in the
catalyst bed, and (e) repeating these steps, whereby the catalysts
of the first layer of the catalyst bed have significant activity
but also a higher capacity for producing coke than the catalyst of
the second layer and whereby the catalysts of the second layer of
the catalyst bed may have the same or different activity as that of
the catalysts of the first catalyst layer, but have a reduced
capacity to make coke.
The different capacities of the catalysts of the different layers
to make coke may be achieved by using various processes to produce
the catalysts and/or compositions of the catalysts of the two
layers. In one embodiment, the composition of the catalyst of the
first layer contains a higher percentage of Cr.sup.6+ components,
by weight, than the catalysts of the second layer. In a further
embodiment, the surface area of the catalyst of the first layer is
greater than that of the catalyst of the second layer. In this
embodiment, the surface area of the catalyst of the first layer is
greater than 90 m.sup.2/g, and preferably greater than 90 m.sup.2/g
to about 120 m.sup.2/g, while the surface area of the catalyst of
the second layer is less than 90 m.sup.2/g and preferably from
about 50 m.sup.2/g to less than 90 m.sup.2/g. These differences in
surface area can be achieved by various processing steps, such as
by calcination in varying percentages of steam.
Other processes of manufacture and compositions of the catalysts
may be utilized to achieve this difference in coke making
capability, all of which are within the scope of this invention, to
maintain the high overall activity of the catalysts of both layers
while reducing the capacity of the catalyst of the second layer to
make coke over the capacity of the catalyst of the first layer.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention is intended for use in
aliphatic hydrocarbon dehydrogenation reactions, specifically for
the production of olefins. These improvements especially apply to
HOUDRY.RTM. dehydrogenation processes, as described, for example,
in U.S. Pat. No. 2,419,997 and U.S. Pat. No. 5,510,557. The
HOUDRY.RTM. process includes a series of process steps wherein the
catalyst bed is evacuated, reduced with a reducing gas, such as
hydrogen, and evacuated. The aliphatic hydrocarbon is then
introduced into the catalyst bed and dehydrogenated. The catalyst
bed is then steamed, purged and regenerated and the cycle is
repeated starting with the reduction cycle. One particularly
preferred utilization for these catalysts is for the conversion of
propane into propylene. The method of the invention preferably
utilizes at least two types of catalysts contained in at least two
layers of the catalyst bed.
It has been discovered that an enhanced adiabatic, non-oxidative
paraffin dehydrogenation process with improved olefin yield can be
achieved if at least two catalysts with different compositions
and/or different methods of production are utilized for the
catalysts contained within the catalyst bed of the invention,
wherein the first catalyst is placed in a first layer of the
catalyst bed, through which the feed stream first passes, and the
second catalyst is placed in a second layer of the catalyst bed,
through which the feed stream passes after passing through the
first catalyst layer.
It has been surprisingly discovered that improvements in the
dehydrogenation process occur, such as higher olefin selectivity
and higher olefin yield, when the catalyst of the first layer has
high activity and a higher capacity for the production of coke than
the catalyst of the second layer, while the catalyst of the second
layer may have the same or a different activity from the catalyst
of the first layer, but exhibits a capacity to make coke which is
reduced from the capacity of the catalyst of the first layer. In a
preferred embodiment, the catalyst in the second layer produces
about 20 wt. percent to about 80 wt. percent less coke than the
catalyst in the first layer. More than two layers of catalysts may
be used, wherein the catalysts of the various layers may have the
same or different compositions, methods of production, performances
and capacities to make coke. Further, the arrangement of the
different catalysts in the catalyst bed can vary as long as the
feed stream contacts the catalyst of the first layer prior to
contacting the catalyst of the second layer. Without being bound by
any particular theory, it is believed that by carefully adjusting
the activity and the capacity to produce coke of the different
catalysts of the catalyst layers, the current invention optimizes
the temperature profile in the catalyst bed and accordingly,
optimizes the performance of the catalysts.
In a preferred embodiment, the current invention is optimized when
the reduction in coke production of the second layer is at least
about 20 wt. percent to about 80 wt. percent, thereby reducing the
layers of catalysts with different capacities which are needed.
Each catalyst layer can be optimized based on requirements of heat
balance and kinetics, which are different depending on the position
and quantity of the catalyst in the catalyst bed, and the
temperature of the feed stream at a particular layer. This improved
dehydrogenation process, in addition to improved olefin selectivity
and improved olefin yield, has additional advantages, such as
reduced instability problems, which are commonly encountered, and
allows the reactor to operate at the highest possible temperature,
thereby generating the highest possible conversion while reducing
the likelihood of hot spot formation, increasing process
selectivity, and yet, still providing stable reactor operations at
high conversion rates.
In a preferred embodiment the catalyst of the first layer comprises
from 50 to about 85 percent, by weight of the total catalysts in
the catalyst bed while the catalyst of the second layer preferably
comprises less than 50 percent to about 15 percent of the
catalysts, by weight, in the catalyst bed.
Various modifications can be made to the composition and method of
production of the catalysts of the first and second layers to
achieve the desired process improvements, all of which are within
the scope of the invention. For example, in one embodiment, both
catalysts comprise from about 70 to about 90% of an alumina
carrier, preferably an eta alumina carrier, and from about 10 to
about 30% by weight of one or more chromium compounds. To reduce
the capacity of the catalyst of the second layer to make coke, the
quantity of Cr.sup.+6 cations in the catalyst of the second layer
is less than is present in the catalyst in the first layer. In one
preferred embodiment, the catalyst of the first layer comprises
greater than 1.1% by weight, preferably at least about 1.2% by
weight, and more preferably at least about 1.5% by weight of
chromium compounds containing Cr.sup.+6 cations, while the catalyst
of the second layer contains chromium compounds with Cr.sup.+6
cations in a quantity less than 1.1% by weight, preferably from
about 0.01 to less than 1.1% by weight.
Alternatively, the catalyst of first layer can be produced by
adding an alkali metal compound, preferably a sodium component, to
the catalyst of the first layer in an amount less than the amount
added to the catalyst of the second layer. In one preferred
embodiment, the amount of the alkali metal compound, preferably a
sodium compound, that is added to the second layer is at least 0.5
to about 0.7%, by weight, calculated as Na.sub.2O, while the amount
added to the first layer is decreased, containing up to a level of
less than 0.5%, by weight, and preferably up to a level less than
0.4%, by weight, calculated as Na.sub.2O. If alkali metal compounds
other than sodium compounds are used, equivalent molar quantities
are used to the quantities of sodium compounds described above.
In another preferred composition, which results in the catalyst of
the second layer producing less coke than the catalyst of the first
layer, the surface area of the catalyst of the second layer is less
than that of the catalyst of the first layer. In a preferred
embodiment the surface area of the catalyst of the first layer is
at least 90 m.sup.2/g, and preferably greater than 90 to about 120
m.sup.2/g, while the surface area of the catalyst of the second
layer is less than 90 m.sup.2/g, preferably about 50 to less than
90 m.sup.2/g, most preferably about 80 to less than 90
m.sup.2/g.
In another preferred process, the pore size distribution of the
catalyst of first and second layers is adjusted so that the
catalyst of the first layer produces more coke than the catalyst of
the second layer. Preferably, this is achieved by the catalyst of
the first layer having smaller pores, on average, than the catalyst
of the second layer.
Another processing step to produce the catalyst of the second layer
with a reduced capacity to make coke is by calcination of the
catalyst of the second layer in a steam/air atmosphere with a steam
concentration preferably in an amount greater than 20% to 100% by
volume, and preferably about 80-100% by volume. In an alternative
process or a process to be used in conjunction with this process,
the catalyst of the first layer can be calcined in a steam/air
atmosphere with added steam in an amount up to no more than 20% by
volume, and more preferably in an atmosphere without any added
steam.
Another modification to the composition of the catalyst of the
first layer which can increase its capacity to produce coke over
the capacity of the catalyst of the second layer is by the addition
of Ni compounds, preferably in an amount from about 0.5 to about
1.7% by weight, calculated as NiO, or by adding Pt compounds in an
amount from 100 ppm to about 10,000 ppm by weight.
Other modifications to the composition or process of production of
the catalysts of the two layers, which are known to those skilled
in the art, can also be used to assure that the catalyst of the
second layer produces coke in an amount less than is produced by
the catalyst of the first layer.
To improve the overall performance of the catalysts of both the
first and the second layer, they may include additional components
which enhance their activity or stability, such as zirconium
compounds, preferably zirconium oxide, in an amount of about 0.1 to
about 5% by weight and preferably from about 0.1 to about 1% by
weight, calculated as ZrO.sub.2, and/or magnesium compounds,
preferably magnesium oxide, in an amount of about 0.1 to about 5%
by weight, and preferably from about 0.1 to about 1% by weight,
calculated as MgO.
Other additives may also be added to either or both of the
catalysts of the catalyst bed, such as silica, cerium compounds and
other additives in an amount of about 0.1 to about 5%, preferably
from about 0.1 to about 1%, by weight.
Further, inert materials may be substituted for the active catalyst
of either or both of the first and second layers in the catalyst
beds.
The present invention is also a method of dehydrogenating a
hydrocarbon feed stream, particularly a feed stream containing C3
to C5 aliphatic hydrocarbons, such as propane, using the catalysts
of the invention. In this process, catalysts of different
composition, or produced by different processes, are loaded within
at least a first and second layer within a catalyst bed within a
reactor. The hot catalyst bed is evacuated and the catalysts are
then reduced using a reducing gas, such as hydrogen, and evacuated
again. An aliphatic hydrocarbon is then fed into the catalyst bed
as part of a gas feed at a preselected flow rate, such that the
feed stream initially contacts the catalyst of the first layer and
then the catalyst of the second layer. Following dehydrogenation,
the catalyst bed is steam purged, regenerated and reduced.
Following reduction, the process steps can be repeated with the
feed stream again.
The current process provides optimization of the performance of the
catalyst bed by utilization of two different catalysts with
different capacities to produce coke in different layers within the
catalyst bed. Without being bound by any particular theory, it is
believed that each catalyst layer optimizes performance based on
the requirements of heat balance and kinetics. The improved process
reduces instability, allows the reactor to operate at a high
reaction temperature resulting in high conversion yet high
selectivity while enhancing the stability of the reactor.
It will be apparent from the foregoing that while particular forms
of the invention have been illustrated, various modifications can
be made without departing from the invention.
* * * * *